remove.cs

...
namespace In2TeamsSplitter.Models
{
    [Table("teammates")]
    public class TeamMateItem : INotifyPropertyChanged
    {
        ...
        public Command RemoveCommand => new Command(Remove);

        private void Remove()
        {
            TeamMatesViewModel.Instance.Value.conn.Delete(this);
            TeamMatesViewModel.Instance.Value.TeamMateSquad.Remove(this);
        }
    }
}